1. Field of the Invention
The present invention relates to methods for forming resist patterns, which being applied over resist patterns of semiconductor devices in order to thicken or to increase the thickness of the resist patterns, thereby forming fine space patterns of which the fineness can surpass a limit in terms of exposure or resolution of light sources in available exposure devices. The present invention also relates to semiconductor devices and production methods thereof.
2. Description of the Related Art
Semiconductor integrated circuits have been highly integrated, and LSIs and VLSIs have been come into practical use. Accompanying this trend, the wiring patterns have been miniaturized down to 0.2 μm or less, and such patterns as small as 0.1 μm or less have been achieved. Lithographic technologies are extremely important in forming fine wiring patterns, in which substrates are coated with resist films, the resist films are selectively exposed and then developed to thereby form resist patterns, thereafter the substrates are dry-etched using the resist patterns as a mask, which are subsequently removed thereby to obtain intended patterns such as wiring patterns. In current lithographic technologies, light sources are demanded for shorter wavelengths and at the same time resist materials with higher resolution are required that can provide suitable properties corresponding to light sources.
However, the development to shorten the wavelength of the exposure lights inevitably involves costly improvement of exposure devices. Furthermore, it is not easy to develop resist materials suitable for shorter wavelengths.
Accordingly, a technology for forming finer patterns is proposed that utilize a resist pattern thickening material (hereinafter, sometimes referred to as “resist swelling agent”), in which resist patterns formed from conventional resist materials are thickened for making finer the space patterns. For instance, a technology so-called RELACS is proposed, in which a resist pattern is formed by exposing a resist of positive resist or negative resist using KrF (krypton fluoride) excimer laser light of wavelength 248 nm of deep ultraviolet light, then a coating film is provided to cover the resist pattern by means of a water-soluble resin composition, the coating film and the resist pattern are made to interact at the interface therebetween using a residual acid within the material of the resist pattern, and the resist pattern is thickened (hereinafter, the thickening sometimes being referred to as “swelling”). In this way, the distance between the resist patterns is shortened, and a fine space pattern is formed. Thereafter, a desired pattern such as a wiring pattern having the same dimension as the space pattern is formed (see Japanese Patent Application Laid-Open (JP-A) No. 10-73927).
However, there exist a problem in the RELACS technology that the ArF excimer laser light cannot be utilized and thus finer wiring patterns cannot be formed by reason that the KrF resists are aromatic resin compositions including a novolak resin, naphthoquinonediazide resin etc., the aromatic ring contained in the aromatic resin compositions allows KrF excimer laser light of wavelength 248 nm to pass through, but absorbs ArF excimer laser light of wavelength 193 nm, i.e. a shorter wavelength, thus inhibits the ArF excimer laser light to pass through. Moreover, there is another problem in the RELACS technology that the resist swelling agent is effective for thickening or swelling the KrF resist but not effective for thickening or swelling the ArF resist. In addition, the resist swelling agent has lower etch resistance itself, thus, when an ArF resist pattern having lower etch resistance is swelled, the same dimension as the swelled pattern cannot be patterned on the substrate to be processed. Furthermore, even if KrF resist having relatively satisfactory etch resistance is swelled there is still another problem that the etching cannot be precisely carried out and patterns having the same dimension as the swelled pattern cannot be obtained, in such cases where etching condition is severe, or where the KrF resist pattern is fine, or where the resist film is thin, or the like.
From the standpoint of forming finer wiring patterns, it is desirable that lights of shorter wavelengths, e.g. ArF excimer laser light, than KrF excimer laser light can be utilized as the light source of the exposure device. When X-rays or electron beams having wavelengths shorter than that of the ArF excimer laser light is used as the exposure light, however, it results in remarkably higher costs and lower productivity. Thus, the utilization of ArF excimer laser light is desired.
Accordingly, the present inventors have proposed, in view of the problem that the resist swelling agent inefficiently work on ArF resist patterns in the RELACS technology, a resist pattern thickening material capable of forming fine patterns by improving affinity with the ArF resist pattern due to a surfactant (see JP-A No. 2003-131400). However, the composition of this resist pattern thickening material is likely to cause a dependency on the pattern size before thickening, that is, when the pattern size before thickening increases, the reduced level of the pattern size after thickening may enlarge in proportion to the pattern size. Furthermore, there appear a difference in the shrinking levels in accordance with the pattern densities, and the pattern sizes after shrinking at relatively dilute regions having longer distances between resist patterns are liable to be different from those at relatively dense regions having shorter distances between resist patterns; more specifically, the more dense are the resist patterns the larger are likely to be the shrinking levels of the pattern size after the thickening.
On the other hand, a method to enhance the thickening level of the KrF resist patterns is proposed in order to uniform the pattern shape and in-plane size in the RELACS technology in which the thickening is repeated plural times using the resist swelling agent (see JP-A No. 2000-298356).
However, the ArF excimer laser light is desired to be utilized in order to miniaturize the wiring patterns still more along with the nowadays still higher integration of the semiconductor integrated circuits.
As described, novel technologies are needed that that can thicken uniformly the resist patterns and form conveniently the fine space patterns or wiring patterns with lower costs independently of the sizes or densities of the resist patterns, even when there exist various sizes and the density fluctuation is significant in the pattern layout, in addition to merely forming fine space patterns by way of thickening the resist patterns.
The present inventors have investigated vigorously to solve the problems described above and have found that when a resin and at least one of benzylalcohol, benzylamine and derivatives thereof are employed as the resist pattern thickening material, the resist patterns can be thickened independently of the size of the resist patterns since the reaction can be easily controlled due to no occurrence of cross-linking reaction, in contrast to previous experiences that resist patterns cannot be thickened without a residual acid when the resist patterns are swelled by previous resist-swelling agents; consequently, the present inventors have invented a resist pattern thickening material that represents less size-dependency.
However, the aforesaid resist pattern thickening material containing benzylalcohol may represent insufficient thickening effect depending on the species of the resist materials and/or may bring about nonuniform thickening effect depending on pattern layouts, although they can show less size-dependency.
The present inventors therefore have investigated vigorously still more to solve the problems and have found as follows: when resist patterns are formed using the resist pattern thickening material containing benzylalcohol, sufficiently desirable thickening effect may be achieved with less depending on sizes or density fluctuation of resist patterns without showing insufficient thickening effect depending on the species of resist materials, provided that at least one of coating, baking and developing of the resist pattern thickening material containing benzylalcohol is carried out plural times when resist patterns are formed using the resist pattern thickening material containing benzylalcohol.